1. Field of the Disclosure
Exemplary embodiments of the present disclosure relate to an electro-mechanical transducer usable as a piezoelectric actuator of an inkjet recording head, a liquid ejection head including the electro-mechanical transducer, and a liquid ejection apparatus including the liquid ejection head.
2. Description of the Background
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional peripherals having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, an inkjet recording apparatus is known that uses a recording head formed with a liquid ejection head (liquid-droplet ejection head) for ejecting droplets of ink.
For example, such a liquid-ejection head (inkjet recording head) of the inkjet recording apparatus may have a configuration like that illustrated in FIG. 1. In FIG. 1, the liquid-ejection head includes a nozzle 102 through which ink droplets are ejected, a pressure chamber 101 (also referred to as, for example, a pressure chamber, ink channel, pressurization liquid chamber, or liquid chamber) connected to the nozzle 102, an electro-mechanical transducer 109, such as a piezoelectric element that pressurizes ink within the pressure chamber 101 (or an electro-thermal conversion element such as a heater), a diaphragm foundation member 105 that forms a wall surface of an ink channel, and an energy generator formed with electrodes facing the diaphragm 105. The energy generator generates energy to compress the ink in the pressure chamber 101, thereby ejecting ink droplets from the nozzle 102. In FIG. 1, a voltage is applied to a lower electrode 106 and an upper electrode 108 of the electro-mechanical transducer 109 to vibrate the electro-mechanical transducer 109, thereby generating the above-mentioned energy. The liquid ejection head further includes a nozzle plate 103, a pressure-chamber substrate (Si substrate) 104, and an electro-mechanical transducer film 107.
Two types of inkjet recording heads are in practical use: an inkjet recording head using a vertical-vibration-type piezoelectric actuator that extends and contracts in an axial direction of an electro-mechanical transducer, and an inkjet recording head using a flexural-vibration-type piezoelectric actuator.
For an inkjet recording head using a flexural-vibration-type piezoelectric actuator, for example, a piezoelectric material layer is uniformly formed over a whole surface of a diaphragm by coating and the piezoelectric material layer is cut into a shape corresponding to a pressure chamber by lithography to form a piezoelectric element, so that pressure chambers are separated from each other.
The piezoelectric element used in the flexural-vibration-type piezoelectric actuator includes, for example, a lower electrode serving as a common electrode common to multiple elements, a lead zirconate titanate (PZT) film (piezoelectric layer) on the lower electrode, an upper electrode serving as an independent electrode formed on the PZT film, an interlayer insulation film formed on the upper electrode that insulates the lower electrode from the upper electrode, and a wire electrically connected to the upper electrode via a contact hole formed in the interlayer insulation film (for example, as in JP-3365485-B and JP-4218309-B.
However, the lower electrode serving as the common electrode described in an exemplary embodiment of the above-mentioned patent documents is a metal electrode containing, for example, Pt. Such an electrode may deteriorate due to dispersion of lead (Pb) contained in PZT, which may degrade fatigue resistance. Further, the desired cohesion of the metal electrode with the piezoelectric layer may not be obtained, causing reduced reliability.
Alternatively, to reduce initial flexure of a diaphragm constituting an inkjet recording head, JP-3019845-B proposes a piezoelectric element (including a lower electrode, a piezoelectric layer, and an upper electrode) that is formed via a diaphragm and in which at least one layer used together the piezoelectric layer is a compression film having compression stress, in which the compression film is a metal oxide film to prevent dispersion of lead.
However, in a case in which the lower electrode is a metal oxide film, the lower electrode is commonly provided for a plurality of piezoelectric elements. Consequently, when the plurality of piezoelectric elements is simultaneously driven to eject a large number of ink droplets at a time, the resulting voltage drop can destabilize the degree of displacement of the independent piezoelectric elements, thus degrading ink ejection characteristics. Further, in a case in which the lower electrode is an oxide electrode, the specific resistance value of the oxide electrode is approximately 101 to 103 times greater than that of the metal electrode, which may easily cause the above-described degraded ejection characteristics.